The thin film transistor (TFT) is formed on the thin film transistor array substrate and is used for controlling the image displaying of the display panel, so that the thin film transistor is an indispensable main component in the liquid crystal display panel.
The thin film transistor array substrate also disposed with a source electrode layer, a drain electrode layer, gate electrode layer and an active layer. In one thin film transistor, when the current on the source electrode layer in the left side flowing to the drain electrode layer in the right side, a channel of the active layer formed in the middle of the active layer is required to penetrate through. Thereby, when the driving voltage is applied to the gate electrode layer under the active layer, an induced electric field is generated from the active layer and controlled the channel of the active layer to be turned on, then the current of the source electrode layer can be circulated to the drain electrode layer. This is the working principle of the thin film transistor array substrate.
The aforementioned thin film transistor array substrate is manufactured on a glass substrate, such manufacturing technique usually employing equipment like physical vapor deposition (PVD), chemical vapor deposition (CVD), other semiconductor process equipment, or the like. Furthermore, the passivation layer of the thin film transistor array substrate may be formed using a method such as plasma enhanced chemical vapor deposition (PECVD). As a switching element in a display device, an amorphous silicon layer or a polycrystalline silicon layer is used for an active layer of a thin film transistor is widely used. Using an amorphous silicon layer to form an active layer of a thin film transistor has problems such as low carrier mobility (less than 1 cm2/V·s) and small on-current. On the other hand, using a polycrystalline silicon layer to form an active layer of a thin film transistor has a problem in that, whereas the carrier mobility is too high (can be 200 cm2/V·s), and thus sufficient switching characteristics of the thin film transistor array substrate cannot be obtained. This problem is subject to process technology to overcome.